Quantification of forest degradation in different forest types of Yellapur forest division of Uttara Kannada district, Karnataka

Introduction

Forest biomass, encompassing all living and dead organic material within these ecosystemssuch as trees, shrubs, roots and soil organic matter is a indicator of forest health and productivity. It plays a crucial role in global carbon cycles by acting as a significant reservoir for carbon, thereby helping to mitigate climate change through the absorption and storage of atmospheric carbon dioxide. Beyond carbon storage, forest biomass supports vital ecosystem functions like nutrient cycling, soil formation and providing habitats for diverse species. Understanding the dynamics of forest biomass is essential for evaluating carbon sequestration potential and assessing the impacts of deforestation and forest degradation on climate change mitigation efforts. Forest degradation, driven by human activities such as deforestation, logging, unsustainable practices, infrastructure development and climate change, leads to a decline in forest health and quality (Hosonuma et al., 2019) [8] . This degradation negatively impacts forestdependent communities, exacerbates socioeconomic inequalities and threatens cultural heritage and indigenous knowledge. Degraded forests are more vulnerable to natural disasters, which can affect human settlements, infrastructure and biodiversity. Between 1990 and 2020, the global forest area decreased by 3%, from 4.24 billion to 4.06 billion hectares (Anon., 2020) [1] . Deforestation and encroachment, driven by population growth and increasing land demand, are key contributors to this decline (Capistrano and Kiker, 1995) [5] .

In India, forest quality declined by over 74,457 sq. km between 2015 and 2021, with significant losses in Karnataka and the northeastern states, highlighting the urgent need for strengthened conservation efforts (Anonymous., 2021) [2] . Forest degradation is a critical environmental issue that affects the ecological balance, biodiversity and the ability of forests to sequester carbon. It refers to the gradual deterioration of forest structure, function and species composition, often driven by human activities such as logging, agricultural expansion, infrastructure development and unsustainable forest management. Unlike deforestation, which results in the complete removal of forest cover, degradation leads to the decline in forest health, resulting in reduced biomass, carbon stocks, tree density and changes in forest dynamics. Tropical and subtropical forests, in particular, are highly susceptible to degradation due to their rich biodiversity and complex ecological interactions. Forest degradation can also be exacerbated by natural factors such as climate change, wildfires and diseases. These changes not only compromise the forest's ability to provide ecosystem services, such as carbon storage, water regulation and habitat for wildlife, but they also diminish the livelihoods of local communities that depend on forest resources. The assessment of forest degradation is a critical endeavour in environmental monitoring and conservation efforts. It involves the systematic evaluation of changes in forest structure, biodiversity and ecosystem functions over time. This often entails the use of standardized methodologies and remote sensing techniques to quantify alterations in forest cover, biomass and carbon stocks. By employing standardized protocols and metrics, researchers and conservationists can effectively monitor the extent and severity of forest degradation, identify hotspots of degradation and develop targeted interventions to mitigate its impacts (Zhuravleva et al., 2013) [24] . Accurate assessment of forest degradation is essential for informing sustainable forest management strategies, enhancing biodiversity conservation efforts and combating climate change.

Materials and Methodology Study area

The present study was focused on various forest types within the Yellapur Forest Division in Uttara Kannada District. Located in the eastern part of the district, the Yellapur Forest Division covers a total area of 168,986.66 hectares, including Betta lands (protected forests), which represents 86.97% of the division's geographical area (1,902.28 km²). The division is bounded by longitudes 74°25' to 75°6' East and latitudes 14°44' to 15°7' North. The study area is depicted in Figure 1. The Yellapur Forest Division encompasses three distinct forest types viz dry deciduous, moist deciduous and semi-evergreen.

Experimental Details

Three permanent plots were established in each of the forest types in the Yellapur division and trees were numbered serially in each plot. The permanent plot was made into 9 subplots (Fig. 2) each having 33.33m x 33.33m indicating a total 27 plots in each forest types. among them, 7 subplots in each forest type were selected for enumeration for assessing the forest degradation. Growth parameters such as girth at breast height, tree height and girth at the base of numbered trees in each plot are recorded. Volume is estimated using the standard formula. An overview of all types of forests. After one year, the same plot is reassessed to record any tree loss, which may have occurred naturally, been caused by human activities, or resulted from other anthropogenic factors. The degradation within the plot is estimated and these findings are then used to assess the total degradation across different forest types based on the area of forest.

Field Data Collection

Observations on various growth parameters is recorded and enumeration is done in the experimental site.

Tree height

The height of the trees was measured from the ground level to the tip of the tree. Ravi altimeter was used for measuring the height of the trees. The tree height was expressed in meters.

Girth at breast height

The girth of the tree was measured at 1.37 m height from ground level. The tape was used to measure the girth. The girth of the tree was expressed in meters.

Girth at the base (GAB)

Girth at the base typically refers to the circumference measurement of the base of a tree taken at 10 cm above ground using tape.

Recording the tree parameter and dead trees

Geographical conditions of the locations, including latitude, longitude and altitude, are recorded using GPS. Additionally, tree parameters are documented and any dead trees present in the field are identified and recorded.  Carbon stock estimation: The total carbon stock was determined by multiplying the total tree biomass with a factor of 0.47 as suggested by IPCC (2007) and expressed in t ha -1 .

Calculation

Carbon stock = Total biomass × 0.47

Experimental results

Annual degradation in tree height

The result pertaining to degradation with respect to tree height has been presented in 2). The statistical analysis indicated that the quantity of degradation in dry deciduous forests is significantly higher as compared to semi-evergreen forests however the quantity of degradation between dry and moist deciduous forests and moist and semi-evergreen forests are on par with each other at a 5 per cent level of significance.

Annual degradation in volume

The The statistical analysis showed that the volume of degradation is notably higher in dry deciduous forests compared to semievergreen forest and the degradation of volume between dry and moist deciduous forests as well as between moist and semi-evergreen forests is similar (Table 2). The statistical analysis revealed that biomass degradation is significantly higher in dry deciduous forests compared to semi-evergreen forests. The degree of biomass degradation between dry and moist deciduous forests as well as between moist and semi-evergreen forests appears to be comparable (Table 3).

Annual degradation in carbon stock

The The statistical analysis found that the loss of carbon stock is much higher in dry deciduous forests compared to semievergreen forests. At the same time, the loss of carbon stock between dry and moist deciduous forests as well as between moist and semi-evergreen forests is fairly similar (Table 3). 4). In the dry deciduous forest out of the 33 recorded dead trees 10 (30.33%) were cut, 9 (27.77) were diseased and 7 (21.21%) were snagged trees (Plate 1). In the moist deciduous forest among the 25 dead trees recorded per hectare 9 (36%) were cut, 8 (32%) were diseased and 4 (16%) snagged trees (Plate 2). In the semi-evergreen forest, the highest number of dead trees were due to natural causes 6 (40%) trees followed by 5 (33.33%) diseased trees, 2 (13.33%) uprooted trees and 2 (13.33%) cut trees (Plate 3) Across all forest types, the most common cause of tree mortality was disease accounting for 22 dead trees followed by cutting (21 trees) and natural causes (14 trees). Statistical analysis indicated that the number of dead trees was significantly higher in the dry deciduous forest compared to the semi-evergreen forest. However, there was no significant difference in the number of dead trees between the dry deciduous and moist deciduous forests, nor between the moist deciduous and semi-evergreen forests (Table 4 and Fig. 3). [22] reported that 84 trees died across four study sites between 1996 and 1999 with an annual mortality rate of 0.73 per cent for the entire forest stand though mortality rates varied among the individual sites. Mueller et al. (2005) [14] predicted that drought frequency and severity would increase across many continental interiors. Their analysis of the impacts on dominant plants identified several major causes of degradation. These include heightened anthropogenic activities, such as logging and land conversion, as well as natural disturbances like droughts and pest infestations. Additionally, changes in land use and insufficient forest management practices have likely intensified the loss of stem density and basal area.

According to a study by Ciais et al. (2008) [7] , increased frequency and severity of droughts can lead to substantial losses in forest biomass and carbon stock due to reduced tree growth and increased mortality rates. Furthermore, anthropogenic pressures, such as logging and land conversion, can exacerbate these effects by removing large amounts of biomass and disrupting the forest ecosystem. Inadequate forest management practices, as highlighted can also contribute to the decline in biomass and carbon stocks by failing to adequately address the impacts of environmental stressors and human activities on forest health.

Long-term observations in the Uttara Kannada district of the Western Ghats have shown that forest areas closer to human settlements and with easier access experience declines in tree density, basal area, biomass and carbon stocks. The increased removal of trees in smaller diameter classes indicates a high demand for these trees by local communities. In less disturbed areas, the higher mortality of smaller trees is due to their inability to compete with taller, canopy trees for resources such as light, moisture and nutrients. Despite natural disturbances and tree harvesting, certain forest plots have seen increases in basal area, biomass and carbon stocks due to the enhanced growth of surviving trees. The resultant canopy gaps have supported new tree recruitment, leading to a restoration of tree density, above-ground biomass and carbon stocks, which partially mitigates CO2 emissions (Bhat and Ravindranath, 2011) [4] . Joshi and Dhyani (2019) [9] are pertinent to my research as their findings reflect how forest structure and human activities influence carbon storage. Variations in carbon stocks are attributed to differences in tree density, basal area, species diversity and both biotic and abiotic factors affecting tree growth. The proximity to mining operations, human disturbances and development projects has resulted in the loss of mature, large trees, thereby affecting forest structure and carbon sequestration. Larger-diameter trees have been identified as key carbon reservoirs. Their work underscores the need to protect mature, large-diameter native trees and offers critical insights for forest managers to create effective management strategies for tropical dry deciduous forests.

Summary and conclusion

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